Attenuation device,particularly pulsation attenutor

ABSTRACT

The invention relates to an attenuation device, particularly a pulsation attenuator, having a casing ( 1 ) defining a fluid chamber ( 11 ) through which a fluid may flow along a flow axis ( 7 ), and having an attenuation element made of a resilient material located within the casing ( 1 ). Said attenuation device is characterized in that the attenuation element has at least two annular bodies ( 15, 17 ) that are disposed in an at least partially overlapping manner, surrounding the flow axis ( 7 ) at least partially.

The invention relates to an attenuation device, particularly a pulsationattenuator, with a casing which defines a fluid chamber through which afluid can flow along a flow axis, and with an attenuation element ofresilient material located in the casing.

Attenuation devices for smoothing of pressure surges in fluid systemsand for reducing the resulting vibrations and noise can be dividedmainly into two known groups of attenuation devices, specifically, onthe one hand, into hydropneumatic attenuators which as hydraulicaccumulators contain an additional gas volume, and, on the other hand,into fluid sound attenuators, so-called silencers, in which without anadditional gas volume an attenuation effect takes place by reflection orabsorption. Reference is made to the technical book “The HydraulicTrainer, Volume 3,” published by Mannesmann Rexroth, pages 106 and 107,for the corresponding prior art.

With hydropneumatic attenuators good properties can be achieved in afrequency band which extends from very low frequencies to about 400 Hz,so that these attenuators would be suited for use in fluid systems inwhich pressure pulsations occur in this frequency band due to operationof hydraulic pumps, their engagement and disengagement processes, and tovalve operating processes. But since these attenuators with additionalgas volume are both bulky and heavy, these attenuation devices cannot beused in many applications where there is very limited installation spaceand a lightweight construction is necessary, as is the case, forexample, in hydraulic systems in motor vehicles. Other disadvantages ofattenuation devices with gas filling are that their attenuation actionvaries depending on the temperature and that the attenuation actionoverall is degraded by gas losses due to permeation.

Conversely, so-called silencers are characterized by comparison by a farmore compact and lightweight construction, but their use is limited bythe attenuation action being sufficient only at higher frequencies ofmore than about 200 Hz. This prevents use in automotive engineeringwhere in hydraulic systems which are assigned to the steering, brakingand stability control system or in active suspension systems, operatingprocesses can take place in a very wide frequency band which extendsfrom very low frequencies to high frequencies of 500 Hz or more.

To solve the aforementioned problems, DE 43 38 912 C1 discloses apressure surge attenuator for reducing hydraulic shocks in fluid lines.In this known solution, the pressure fluctuations which are coupled tothe compressive gas volume which acts as a resilient attenuation elementin hydropneumatically operating attenuators are coupled to a resilientmaterial. This yields a frequency behavior which is similar to thehydropneumatic attenuators, at a conversely reduced size and reducedweight; but it has been shown that an adequate attenuation action cannotbe achieved by means of this known solution.

With respect to this prior art, the object of the invention is to makeavailable an attenuation device which in spite of a compact andlightweight construction, as is necessary for use in automotiveengineering, is characterized by especially good attenuation action.

According to the invention, this object is achieved by an attenuationdevice which has the features of claim 1 in its entirety.

Accordingly, one essential feature of the invention consists in thatinstead of a uniform body which is located in the fluid chamber, as isused in the prior art as the attenuation element, according to theinvention, there is an attenuation element composed of a combination ofannular bodies. This combination of resilient bodies allows spring pathsand spring characteristics which ensure optimum attenuation action whenmatched to a given frequency band.

In the configuration of the attenuation element there can be annularbodies with the same axial length and/or annular bodies with the sameradial thickness relative to the flow axis, depending on theconstruction circumstances or the desired behavior of thecharacteristics.

Here the arrangement can be made such that the annular bodies arearranged adjoining one another on top of one another.

If, in this connection, pairs of annular bodies of different materials,for example of different density and thus resilience of variedintensity, are used, preferably the inner annular body of each pair ofannular bodies which is nearer the flow axis can be formed from amaterial of greater resilience than is the case for the annular bodylocated above. With the corresponding material combinations the desiredbehavior of the characteristics, for example a progressive behavior, canbe implemented.

In preferred embodiments the annular bodies have an uninterrupted,closed annular shape, and the annular bodies can have an annular shapewhich is concentric to the flow axis.

In order to achieve optimum attenuation action, there can be severalpairs of annular bodies surrounding one another in succession in theaxial direction of the flow axis, and in turn with respect to densityand resilience of the material, there can be pairs of rings of differentproperties.

In especially advantageous embodiments the casing forms an enclosure forthe respective outer annular body of the attenuation element.

Here, the arrangement can be such that the casing has a wall whichseparates the attenuation element fluid-tight from the fluid chamber sothat the casing has a double-walled configuration with an inner wallbordering the fluid chamber and an outer wall which is located above theannular body which is the outer one at the time.

If, in this connection, the respectively inner annular body of theattenuation element adjoins the inner wall of the casing which bordersthe fluid chamber, for the annular bodies there is a chamberedarrangement between the wall bordering the fluid chamber and the outerwall of the casing which adjoins the outer annular body.

In the exemplary embodiments in which the casing separates the fluidchamber fluid-tight from the attenuation element, the material of theannular bodies can be an open-pore or cellular material.

The material can be, for example, a PU foam or a synthetic rubber,particularly ethylene-propylene-diene rubber (EPDM), preferably foamedEPDM.

Suitable material of the casing can be oil-resistant and fuel-resistanceelastomers, for example a fluorinated rubber material, particularlybased on vinylidene fluoride-hexafluoropropylene copolymerizates.

The invention is detailed below using the exemplary embodiments shown inthe drawings.

FIG. 1 shows a schematically simplified longitudinal section of oneexemplary embodiment of the attenuation device according to theinvention;

FIG. 2 shows a longitudinal section which corresponds to FIG. 1, theindividual parts, however, being shown in an exploded view, and

FIG. 3 shows a longitudinal section of a second exemplary embodiment ofthe attenuation device similar to FIG. 1.

In the two exemplary embodiments shown in the drawings, the attenuationdevice has a casing 1 of oil-resistant and fuel-resistant elastomermaterial, for example of synthetic rubber. These examples arefluorinated rubber material based on vinylidenefluoride-hexafluoropropylene copolymerizates. This material iscommercially available under the trade name Viton®. It goes withoutsaying that instead of elastomers other types of materials can be used,for example a metallic material which could form the casing.

As is most clearly illustrated in FIG. 2, the casing 1 is made as adouble-walled hollow cylinder, with a circularly cylindrical inner wall3 and a circularly cylindrical outer wall 5 which are concentric to anaxis 7. The latter constitutes the flow axis for the flow of a fluidstream which is to be attenuated and which is flowing into the innerfluid chamber 11 via an opening 9 which is provided in the end wall ofthe casing 1.

Between the inner wall 3 and the outer wall 5 there is a chamber 13 inthe form of an annulus in which the actual attenuation material is heldchambered in the illustrated examples. As FIG. 2 shows most clearly,here it is a combination of foam inserts, this combination being formedfrom three pairs of annular bodies located on top of one another,specifically one inner annular body 15 and one outer annular body 17 ata time.

In the two illustrated exemplary embodiments the annular bodies 15, 17are closed, round rings which are located on top of one another inalignment and adjoining one another, the inner annular body 15 and outerannular body 17 of each pair having the same radial thickness and thesame axial length.

Alternatively, the annular bodies could be of different radialthicknesses and/or different axial lengths. Instead of closed,uninterrupted annular bodies they could be annular bodies composed ofindividual annular segments.

While the pairs of annular bodies are arranged axially abutting oneanother as is shown in FIG. 1, there could be gaps between successivepairs of annular bodies.

In the example from FIGS. 1 and 2, the casing 1 is closed on the endopposite the opening 9 by a cover 19 which is formed from the samematerial as the remaining part of the casing 1. The cover 19 has anannular edge which projects axially to the inside and which engagesappropriately as a sealing part of the chambers 13 between the innerwall 3 and outer wall 5 and is fixed at bonding sites 23 (see FIG. 1).The cement can be a two-component adhesive. The cover 19 has an opening25 which corresponds to the opening 9 for fluid flow.

The exemplary embodiment as shown in FIG. 3 conversely differs only inthat the casing 1 does not have a cover on the end of the fluid chamber11 opposite the opening 9. Instead, the outer wall 5 of the casing 1 asa termination of the chamber which holds the annular bodies 15 and 17has an end-side wall part 27 which is drawn radially to the inside andwhich is cemented to the inner wall 3 via the bonding site 23. As in thefirst embodiment, by means of the bonding site 23, fluid-tight sealingof the chambers 13 containing the pairs of annular bodies is formed.This fluid-tight separation yields free selection possibilities withrespect to use of attenuation materials. Thus both closed-pore materialsand also open-pore or cellular materials can be used. Advantageously PUfoams or synthetic rubbers such as ethylene-propylene-diene rubber(EPDM), preferably foamed EPDM, can be provided. As already noted,instead of the illustrated uniform pairs of annular bodies, there canannular bodies in a different number and in a different unalignedarrangement on top of one another. In particular, the resilience whichis determined, for example, by the material density for the innerannular bodies 15 and the outer annular bodies 17 is chosen to bedifferent in order to achieve the desired attenuation characteristicsmatched to the prevailing frequency band, preferably the inner annularbodies 15 nearer the fluid chamber 11 having greater resilience than theouter annular bodies 17 supporting them on the outside. The pairs ofannular bodies following one another in the axial direction can alsohave different resilience. Furthermore, the casing 1 could be structuredsuch that especially at an elevated pressure level, the outer wall 5 asthe support of the outer annular bodies 17 has a rigid structure (forexample metallic structure), while the inner wall 3 is formed from aresilient elastomer in order to effectively couple the pressure surgesto the attenuation material.

The casing of the body 17 can also be applied by means of specialenamels (coatings) in an immersion, painting or spraying process. Theseenamels are based, for example, on HNBR or Viton®. A layer of more orless any thickness can be applied by repeated immersion or sprayinguntil a fluid-tight and resistant layer has been applied.

1. An attenuation device, particularly a pulsation attenuator, with acasing (1) which defines a fluid chamber (11) through which a fluid canflow along a flow axis (7), and with an attenuation element of resilientmaterial located in the casing, characterized in that the attenuationelement has at least two annular bodies (15, 17) which are located atleast partially on top of one another and which at least partiallysurround the flow axis (7).
 2. The attenuation device according to claim1, characterized in that the annular bodies (15, 17) have the same axiallength.
 3. The attenuation device according to claim 1, characterized inthat the annular bodies (15, 17) have the same radial thickness.
 4. Theattenuation device according to claim 1, characterized in that theannular bodies (15, 17) are arranged adjoining one another on top of oneanother.
 5. The attenuation device according to claim 1, characterizedin that the inner annular body (15) of each pair of annular bodies whichis nearer the flow axis (7) is formed from a material which has greaterresilience than the material of the overlying annular body (17).
 6. Theattenuation device according to claim 1, characterized in that theannular bodies (15, 17) have an uninterrupted, closed annular shape. 7.The attenuation device according to claim 1, characterized in that theannular bodies (15, 17) have an annular shape which is concentric to theflow axis (7).
 8. The attenuation device according to claim 1,characterized in that there are at least two pairs of annular bodies(15, 17) surrounding one another in succession in the axial direction ofthe flow axis (7).
 9. The attenuation device according to claim 1,characterized in that the casing (1) forms an enclosure for therespective outer annular body (17) of the attenuation element.
 10. Theattenuation device according to claim 1, characterized in that thecasing (1) has a wall which separates the fluid chamber (11) from theattenuation element fluid-tight.
 11. The attenuation device according toclaim 10, characterized in that the respectively inner annular body (10)of the attenuation element adjoins the wall (3) of the casing (1)bordering the fluid chamber (11) opposite the attenuation element. 12.The attenuation device according to claim 11, characterized in that theannular bodies (15, 17) of the attenuation element are chambered betweenthe wall (3) of the casing (1) bordering the fluid chamber (11) and theouter wall (5) of the casing (1) adjoining the outer annular body (17).13. The attenuation device according to claim 1, characterized in thatthe attenuation material of the annular bodies (15, 17) is an open-poreor cellular material.
 14. The attenuation device according to claim 1,characterized in that the attenuation material of the annular bodies(15, 17) is a closed-pore material.
 15. The attenuation device accordingto claim 1, characterized in that the attenuation material is a plasticmaterial.
 16. The attenuation device according to claim 15,characterized in that the attenuation material is a PU foam.
 17. Theattenuation device according to claim 15, characterized in that theattenuation material is a synthetic rubber, in particularethylene-propylene-diene rubber (EPDM), preferably foamed EPDM.
 18. Theattenuation device according to claim 1, characterized in that thematerial of the casing (1) is a fluorinated rubber material, inparticular based on vinylidene fluoride-hexafluoropropylenecopolymerizates.